"We used to think that we had cancellous bone for the same reasons that we use foams in engineering, to absorb energy or make the structure more lightweight, but it turns out that cancellous bone does something different, the way cancellous bone breaks actually makes it heal better," says Christopher Hernandez. (Credit: Francisco Daum/Flickr)

When most things break, they fall apart and lose their mechanical function. But a foam-like type of bone can recover shape after it breaks.

Called cancellous bone, it’s found near joints and in the vertebrae.

A microscopic slide showing a region of cancellous bone (blue). The brighter blue regions are more brittle regions where we found cracks more likely to grow. (Credit: Cornell)An image of cancellous bone with regions of microscopic tissue damage shown in green and orange. (Credit: Cornell)An image of a high-resolution finite element model of cancellous bone is shown. The color map indicates the distribution of mechanical stress (red means a highly stressed location). (Credit: Cornell)

“Cancellous bone does the opposite, it has softer surfaces with a more brittle interior,” says Christopher Hernandez, associate professor of engineering at Cornell University.

The combination of softer surfaces and brittle interior allows cancellous bone to direct cracks to locations where they are less detrimental, allowing the structure to recover its shape—bounce back—after it breaks.

“That’s totally not what we expected from an engineering standpoint,” says Ashley Torres, a graduate student in biomedical engineering, who was one of two individuals to lead the study. “But it allows the material to continue to function after failure.”

The discovery provides a compelling answer to the long-standing question as to why bones have foam-like regions.

“We used to think that we had cancellous bone for the same reasons that we use foams in engineering, to absorb energy or make the structure more lightweight, but it turns out that cancellous bone does something different, the way cancellous bone breaks actually makes it heal better,” says Hernandez.

“In the future, this could help in the design of new materials that can take advantage of this ‘function after failure,'” says Jonathan Matheny the other graduate student leading the project.

Material heterogeneity in structures, the group proposes, could help mitigate the effects of small structural flaws that are inevitable in manufacturing. Additionally, Matheny says these findings have implications for medicine, “to help us identify people at risk for an osteoporosis-related fracture and prescribe drug treatment.”